I need to find magnitudes of forces

1. Feb 16, 2010

Ryuk1990

1. The problem statement, all variables and given/known data

I got a resultant force 28 degrees to the right of the positive y axis. The resultant value is 4200 N. There is one force 45 degrees to the right of the resultant force. The second force is 20 degrees to the left of the positive y axis. All I want to know is how I'm supposed to set up the equations so that I can solve for the two force components.

3. The attempt at a solution

I started out by calculating that there is 17 degrees between the positive x axis and the first force component.

Is this how I'm supposed to set up the equations?

Force X: F1*cos17o + 4200*sin28o - F2*cos20o = 0

Force Y: F1*sin17o + 4200*cos28o + F2*cos20o = 0

2. Feb 16, 2010

rl.bhat

You are right.

3. Feb 16, 2010

Ryuk1990

Ok, just one more thing. Can you explain to me the theory behind this? I don't get why I have to set X and Y forces to 0.

If I plug in 0 and 0 for the resultant formula which is R = $$\sqrt{FX^2 + FY^2}$$, that doesn't equal 4200 which is what the resultant force is. This confuses me.